[Learning French] Je sèche

“Je sèche.” can only be used alone :

you can’t say : je sèche “something”

It means something like “No idea”, “I don’t know what I can’t do to go on (the exercice)”‘.
(I found: “dry up” in my dictionnary)

ref. http://forum.wordreference.com/showthread.php?t=314927&langid=6